This invention relates to catalyst components for the polymerization of alpha-olefins, and more particularly, to a method for improving the polymerization performance of organoaluminum reduced, electron donor complexed, brown solid beta titanium trichloride compositions in terms of polymer particle size.
Commonly assigned U.S. Pat. Nos. 3,984,350 (Karayannis et al.), 4,111,836 (Karayannis et al.), and application Ser. No. 892,663 (filed Apr. 3, 1978, in the name of Nicholas M. Karayannis and Harold Grams) disclose high surface area, large pore volume brown solid catalyst components comprising beta titanium trichloride and an amount, ranging up to about 10 mole percent, of at least one electron pair donor, such brown solid catalyst components being prepared by reducing titanium tetrachloride with an organoaluminum component followed by complexing the reduced solid with at least one electron pair donor and treating the result with at least one electron pair acceptor. For purposes hereof, the brown solid catalyst components disclosed in the aforesaid patents and application are referred to as "organoaluminum reduced, electron donor complexed, brown solid, beta titanium trichloride."
When used in the polymerization of alpha-olefins, catalysts containing organoaluminum reduced, electron donor complexed, brown solid, beta titanium trichloride give highly desirable results in terms of activity and stereospecificity such that high yields of highly crystalline polymeric products are obtained. However, such brown solid titanium trichloride compositions, being somewhat fragile, are susceptible to substantial attrition during normal catalyst makeup and pumping operations as well as during polymerization such that decreases in the particle size of the brown solid often occur. Solid polymer produced in the presence of the attritted brown solid often is reduced in terms of particle size and bulk density. Additionally, attrition can lead to production of undesirably high levels of fine polymer particles. Polymer particle size, bulk density, and fines content are important from the standpoint of product quality because if particle size and/or bulk density are too low and/or levels of fines are too high, difficulties in handling and processing the polymeric products are encountered. Fines also are disadvantageous from the standpoint of process efficiency because they can accumulate in process lines and equipment to such an extent as to cause plugging.
In the vapor phase polymerization of alpha-olefins using catalysts containing organoaluminum reduced, electron donor complexed, brown solid, beta titanium trichloride a further difficulty is encountered due to the high activity of the catalysts. When catalyst is introduced into the vapor phase reactor, contact between gaseous alpha-olefin monomer and catalyst can lead to a violent, exothermic, initial polymerization reaction. Heat evolved due to this initial reaction often is sufficient to cause fusion of polymer into agglomerates. Formation of these agglomerates is undesirable from the standpoint of handling and processing of the polymeric product, and in addition, if large enough agglomerates form they can seriously hinder reactor performance.
It is an object of the present invention to provide a method for improving the alpha-olefin polymerization performance of organoaluminum reduced, electron donor complexed, brown solid, beta titanium trichloride catalyst components in terms of polymer particle size. A further object of the invention is to provide a method for improving such brown solid catalyst components in terms of resistance to attrition such that polyalphaolefins produced in the presence thereof are improved in terms of particle size, bulk density, and fines content. A further object of the invention is to provide a method for preparing a brown solid catalyst component which, when used in the polymerization of alpha-olefins, is essentially comparable to the brown solid catalyst components disclosed in U.S. Pat. Nos. 3,984,350 and 4,111,836, and application Ser. No. 892,663 in terms of overall activity but reduced in terms of initial activity such that high yields of polyalpha-olefins can be produced in vapor phase polymerization systems without substantial agglomerate formation. Other objects of the invention will be apparent to persons to skill in the art from the following description.
It has been found that the foregoing objects can be attained according to the present invention wherein the brown solid, beta titanium trichloride catalyst components of the aforesaid U.S. Pat. Nos. 3,984,350, 4,111,836, and application Ser. No. 892,663 are contacted with alpha-olefin monomer and aluminum alkyl catalyst component in amounts and under conditions such that a low yield polyalpha-olefin structure is formed around the brown solid catalyst component. The polyalpha-olefin structure surrounding the brown solid catalyst component protects the same from attrition during polymerization use such that substantial reductions in polymer particle size and bulk density are avoided. Further, although the plastic structure which encapsulates the brown solid has only minor effects on overall polymerization activity, initial activity is reduced such that on introduction into a vapor phase polymerization zone, violent exothermic polymerization and the accompanying agglomerate formation are reduced.
Heretofore it has been proposed to treat various titanium halide alpha-olefin polymerization catalyst components with aluminum alkyls and alpha-olefins for various purposes. However, these proposals do not disclose the process of the present invention wherein the polymerization performance of organoaluminum reduced, electron donor complexed, brown solid, beta titanium trichloride catalyst components prepared in accordance with U.S. Pat. Nos. 3,984,350, 4,111,836, and application Ser. No. 892,663 are improved in terms of polymer particle size by treatment of the brown solid, prior to polymerization use, with aluminum alkyls and alpha-olefins. For example, British Pat. No. 1,444,010 (Solvay) discloses that titanium trichloride compositions prepared by reduction of titanium trichloride with organoaluminum components followed by complexing with electron donors and treatment with titanium tetrachloride can be improved in terms of shelf life by preactivation treatment with organoaluminum compounds in an inert solvent with 10 hours of preparation. The titanium trichloride compositions to be preactivated according to this patent "may be, although they are not necessarily based on a TiCl.sub.3 of violet colour, belonging to the delta crystalline form according to the classification generally adopted." As an optional feature of the invention, the patentee discloses that the titanium trichloride composition can be contacted with at least one alpha-olefin simultaneously with or subsequent to the organoaluminum preactivation. Contacting with alpha-olefin is conducted at -10.degree. to 100.degree. C. and 1-50 atmospheres for a period of time such that up to 1,000 parts by weight of polyalpha-olefin are formed per part by weight of the preactivated titanium trichloride composition. British Pat. No. 1,444,009 (Solvay) discloses the identical preactivation treatment and optional prepolymerization for titanium trichloride compositions having a surface area of at least 75 square meters per gram and a pore volume of at least 0.15 cc per gram and which "may be, although they are not necessarily, based on a TiCl.sub.3 of violet colour, belonging to the delta crystalline form according to the classification generally adopted."
U.S. Pat. No. 4,086,185 (Shirai et al.) discloses that the polymerization performance of delta titanium trichloride compositions prepared by a variety of methods, including reduction of titanium tetrachloride with organoaluminum compounds followed by complexing with electron donors and treatment with titanium tetrachloride, can be improved in terms of stereospecificity by contacting the delta titanium trichloride composition, prior to polymerization use, with an alkylaluminum halide and propylene at 10.degree. to about 50.degree. C. to form 0.5 to 5 parts by weight polypropylene per part by weight delta titanium trichloride composition. To like effect is Japan Kokai No. 53-031787 (Chisso).
U.S. Pat. No. 3,893,989 (Liecht et al.) discloses that the alpha-olefin polymerization performance of violet titanium trichloride prepared by reduction of titanium tetrachloride with organoaluminum compounds can be improved in terms of particle size distribution by a staged polymerization wherein propylene is first polymerized in the presence of an aluminum alkyl catalyst component and the violet titanium trichloride at 15.degree.-25.degree. C. and then additional propylene is polymerized in the presence of the resulting slurry of polypropylene and catalyst at temperatures ranging from 40.degree.-90.degree. C.
Other prior art which may be of interest to the present invention in disclosing pretreatment of various alpha-olefin polymerization catalysts and/or catalyst components includes U.S. Pat. Nos. 2,936,302 (Jones et al.); 2,956,994 (Peterlein); 2,990,399 (Peterlein); 3,035,037 (Rindtorff et al.); 3,062,801 (Hoeg et al.); 3,067,183 (Hagemeyer et al.); 3,272,788 (Dietz); 3,275,613 (Emrick et al.); 3,365,436 (Ourgaud); 3,514,501 (Leibson et al.); and 3,780,136 (Khelghatian et al.). None of these patents, however, discloses application of the treatment to titanium trichloride compositions prepared by reduction of titanium tetrachloride with an organoaluminum component followed by complexing with electron donors and treatment with electron acceptors.